Various optical recording media including a rewritable DVD and a recordable DVD are recently recognized widely as an external storage for information processing apparatus such as a computer because these optical recording media can store large-capacity information and are capable of easy random access. For example, a typical recordable DVD and the like comprising a recording layer comprising an organic dye has a multilayer structure which comprises an organic-dye recording layer and a reflective layer placed in this order on a transparent disk substrate and further comprises a protective layer with which the recording layer and the reflective layer are covered. In such recording media, recording/reading is performed with a laser light through the transparent disk substrate (resin substrate). These optical recording media comprising a recording layer comprising an organic dye are known to increase in error due to the influence of water present at the interface between the organic-dye layer and the reflective layer (see patent document 1).
Optical recording media intended to prevent such increase in error have been proposed which include: an optical recording medium comprising a first reflective layer of gold or a gold alloy laminated on an organic-dye recording layer and a second reflective layer of a silver alloy or copper alloy laminated on the first reflective layer (patent document 1); and an optical recording medium which comprises a thin metallic interlayer made of Pd, Ni, Sn, Au, In, Te, Si, Ge, or an alloy of any of these placed on an organic-dye recording layer and a reflective layer of silver or a silver alloy placed on the interlayer (patent document 2).
Incidentally, an optical recording apparatus retains a recording condition optimized beforehand for various optical recording media, and use of the recording condition enables satisfactory recording. The recording media to be used vary in reflectance and thermal conductivity depending on the kind of the reflective layer (e.g., the material and thickness of the reflective layer). Because of this, a different recording condition is used for a disk differing in reflective layer.
In the recordable DVD and CD-R disc which are mainly used presently, most disks employ a reflective layer made of silver or an alloy comprising silver as a main component. Because of this, the recording condition originally possessed in the optical recording apparatus has been optimized for a silver reflective layer. There has hence been a possibility that optical recording media such as those described in patent document 1 and patent document 2 cannot have satisfactory recording characteristics when used under the recording condition originally possessed in the optical recording apparatus and optimized for the optical recording media employing a silver reflective layer. Furthermore, since the reflective layer of those optical recording media has a lower reflectance than the silver reflective layer due to the constitutions thereof, there has been a possibility that sufficient recording characteristics cannot be obtained or the choice of a recording material might be narrowed. In addition, especially in high-speed recording, it is necessary to reduce thermal interference to widen a margin of recording characteristics.
However, this necessitates a reduction in the film thickness of the dye recording layer, resulting in a decrease in reflectance.
There has hence been a possibility that it might be difficult to maintain recording characteristics.
On the other hand, a technique is known in which a first reflective layer made of a pure metal and having a high reflectance and a second reflective layer having a lower thermal conductivity than the first reflective layer are laminated on a light-absorbing layer comprising an organic dye to thereby reconcile power margin in high-speed recording and reflectance (reference document 3). This is intended to obtain a practical level of reflectance with the first reflective layer and to lower the overall thermal conductivity with a lowly thermally conductive material of the second reflective layer. In this case, however, the first reflective layer has a film thickness reduced to 50 nm or smaller in order to enhance the effect produced by the thermal conductivity of the second reflective layer, and there is hence a problem that a decrease in reflectance in some degree is unavoidable. Furthermore, in view of the current situation in which optical recording apparatus optimized for an optical disk employing a silver reflective layer have already spread, there has been a possibility that optical recording media having that constitution cannot have satisfactory characteristics under the recording condition originally possessed in the optical recording apparatus because these recording media require different recording characteristics.
An optical recording medium employing a reflective layer constituted of a single layer of gold or an alloy thereof has also been proposed. A gold reflective layer is known to be an exceedingly satisfactory reflective layer because of the chemical stability thereof. However, there has been a possibility that the optical recording medium employing a gold reflective layer cannot have satisfactory recording characteristics when used with the optical recording apparatus which have already spread, as stated above. In addition, since gold has a poor affinity for an organic-dye recording layer, there has been a possibility that interfacial separation between the reflective layer and the recording layer might occur to cause errors.
Patent Document 1: JP-A-2001-184716
Patent Document 2: JP-A-11-232695
Patent Document 3: JP-A-2001-035014